The goal of this proposal is to elucidate the molecular mechanisms underlying ethanol action in the Drosophila brain. Towards this end I have developed an assay system for acute and chronic tolerance to the sedative effects of ethanol. Using this assay and microarrays, I have identified several genes that exhibit a change in gene expression upon acute and/or chronic exposure to ethanol. Homer, a putative scaffolding protein, and Ypsilon Schachtel (YPS), an RNA binding protein were chosen for further characterization. Preliminary data show that Drosophila mutants of the Homer and YPS genes exhibit decreased and increased ethanol sensitivity, respectively, suggesting that Homer and YPS mediate some of the behavioral effects of ethanol. To determine whether Homer and YPS play a role in regulating ethanol sensitivity and tolerance in Drosophila, the following aims will be pursued: 1) Determine whether the ethanol phenotypes observed in Homer and YPS mutant flies can be rescued using Homer or YPS genomic constructs. 2) Determine whether the ethanol phenotypes observed in the Homer and YPS mutant flies are the result of a change in ethanol absorption/metabolism. 3) Identify the Homer and YPS spatial and temporal expression requirements for rescue of the ethanol phenotypes using the GAL4/UAS and TARGET systems. 4) Determine whether mutants of Homer and YPS have defects in learning and memory and/or locomotor activity.